2. Material and methods
2.1. Analytical instruments and reagents
Melting points were determined on a YanacoMP-S3 micro melting point apparatus without the correction of thermometer. Optical
rotations were measured on a Perkin-Elmer 241 MC polarimeter.
The UV spectra were taken on a HP 8451A diode array spectrophotometer. IR spectra were recorded on a NEXUS-470 spectrophotometer. 1D and 2D NMR spectral data were recorded on Brucker
ACF-300P or Brucker ACF-500P spectrometers in CDCl3. Exact
masses (HRESIMS) were measured by a Waters Synapt HDMS
system. Materials for column chromatography and TLC were silica
gel H (200–300 mesh) and silica gel G (100–200 mesh) (Qingdao